WhatsApp Interest List for Black Friday: How to Build It

Key takeaways

Having someone's phone number is not having permission: the WhatsApp Business policy requires opt-in for any proactive message.
Since July 1, 2025, Meta charges per delivered template message; free-form messages only work inside the 24-hour window opened by the customer.
Anyone who arrives through a click-to-WhatsApp ad and gets a reply within 24 hours opens a free 72-hour window, counted from the company's reply.
Record four fields per contact: opt-in date, source, interest, and contact preference.
Before each send, remove those who already bought, those who asked to leave, and those looking for an item outside the offer.

Why is an interest list worth more than a phone list?

Because an interest list measures current intent, while a phone list only measures history. Someone waiting for your offer replies; someone who signed up for a giveaway two years ago does not.

According to Opinion Box (2025), 60% of Brazilians have already bought through WhatsApp and 82% already communicate with brands through the app. The Panorama Mobile Time/Opinion Box survey (2026) shows WhatsApp on 98.3% of the country's smartphones. Reach is not the problem; the problem is messaging people who did not ask and burning your number before the big day.

Decision rule: if the person did not write to you or reply "I want in," they are not on the list; they need a new invitation.

What opt-in on WhatsApp is and how to record it without mistakes

Opt-in is the explicit authorization a person gives to receive messages from your company outside a conversation they started themselves. The WhatsApp Business Messaging Policy (Meta) prohibits unsolicited messages. Record four pieces of information per contact:

Date and time the person authorized it.
Source: ad, Instagram link, physical store, previous customer.
Invitation text they accepted, so the message on the day matches the promise.
Declared interest: product, category, or service.

Three rules: if the person replied "yes" to a clear invitation, record opt-in and interest. If they only clicked the ad and did not write, there is no opt-in. If they asked to leave, remove them immediately.

A WhatsApp CRM with tags and a per-lead history, such as RASTRO, keeps these fields without a side spreadsheet; the record must exist before the send.

How the 24-hour and 72-hour windows change the cost of the list

The windows define what you can send and how much you pay. According to the WhatsApp Business Platform pricing documentation (Meta, 2025):

24-hour customer service window: opens when the customer writes. Inside it, the company sends free-form messages; outside it, only template messages, charged when delivered.
72-hour entry point window: if the customer arrives through a click-to-WhatsApp ad or the Page's button and the company replies within 24 hours, a 72-hour window opens, counted from the company's reply, in which any message is free. It applies only to clicks made in the Android and iOS apps.
The two windows are independent: one does not extend the other.

These rules belong to the Platform (API); in the WhatsApp Business app, opt-in is equally mandatory.

Contact situation	What can be sent	Cost under Meta's rule (2025)
Wrote less than 24 hours ago	Free-form or template message	Free-form at no charge; template charged
Came from an in-app ad, answered within 24 h, inside the 72 h	Any message	Free
Wrote more than 24 hours ago, no active 72 h	Approved template only	Charged per delivered message
Never wrote and gave no opt-in	Nothing	Prohibited by policy

Consequence: a list built in October will have no open window in November. On the day of the offer you will pay per delivered template, or you will need the person to write to you again. That is why the invitation should ask the person to take an action on the day.

How to invite people to the list

The invitation works when it promises something specific and asks for a reply. "Join our VIP list" does not say what the person gets; "reply YES and get the Black Friday prices at 8 a.m. on Friday" does.

Click-to-WhatsApp ad: the only door that opens the free 72-hour window, as long as the team replies within 24 hours.
Trackable link on Instagram, the website, and email, with a source parameter.
Physical store: QR code with the invitation text; source "store."
Previous customers: only with a new invitation in an active conversation or through an approved template.
People who asked and did not buy in the last 30 days: ask whether they want to be notified.

To define what will be promised, see how to build a clear offer on WhatsApp; for the right week for each door, the 30-day plan.

How to segment the list without asking for too much data

Segment by relationship with the company, interest, and priority. Do not ask for CPF (Brazilian taxpayer ID), address, or income to join a promotion list.

Segment	How to identify	What changes in the message
Previous customer	Bought in the last 12 months	Mention the item bought and the complementary item on offer
New prospect	Never bought, asked for information	Explain the offer and deadline without assuming prior knowledge
Interested in an item outside the offer	Asked for a product with no discount	Tell them transparently before the general send
Asked to leave	Recorded in the history	No message

Rule: a segment with fewer than 20 people does not get its own message; merge it with the closest one. With hundreds of contacts, check how to size your customer service team.

Hypothetical example: 300 interested people, what happens on the day

The numbers below are hypothetical and show the reasoning, not an expected result.

Composition. 300 people gave opt-in in November: 120 came from ads and were answered within 24 hours; 180 came from links and the store.
Free window. Of the 120 from ads, only those answered in the previous 3 days are inside the 72 hours: say 40. The other 260 receive a template charged per delivery.
Cleanup. 25 already bought in the pre-sale, 10 asked to leave, 15 wanted an item with no discount. 250 eligible contacts remain.
Replies. 250 sent, 60 replies. Reply rate = 60 ÷ 250 = 24%.
Conversion. 15 of the 60 buy. Reply to sale = 15 ÷ 60 = 25%; list to sale = 15 ÷ 250 = 6%.
Revenue. Average order value of R$ 180 × 15 = R$ 2,700. Compare it with the cost of the templates (Meta's rate card for your category) and with customer service hours.

Lesson: the correct denominator is 250, not 300.

Common mistakes when building the interest list

Buying or "borrowing" a list. Nobody there gave you opt-in; it violates Meta's policy and triggers blocks that hurt the number's reputation.
Treating silence as authorization. "If you don't reply, I'll assume you accept" is not opt-in.
Forgetting to remove those who already bought. A discount for someone who paid full price two days ago leads to a refund request.
Leaving the ad running without a team. Without a reply within 24 hours, the 72-hour window does not open and the message on the day starts to cost money.
Promising something different from the offer. Under art. 30 of the Brazilian Consumer Protection Code (CDC, Law 8.078/1990), the offer binds the seller; "up to 70% off" with a single item at 70% is misleading advertising under art. 37.

What to measure in the list before, during, and after

Measure four indicators with the same denominator. The ranges are practical references, not market benchmarks.

Opt-in rate = accepted ÷ received the invitation. Below 10% on ads, the invitation is vague or the audience is wrong.
Reply rate on the day = replies ÷ eligible messages. Below 10%, the offer did not deliver what was promised.
Opt-out rate = requests to leave ÷ messages sent. Above 3% in one send, stop and review frequency and segmentation.
Source coverage = contacts with a recorded source ÷ total. Below 80%, the per-channel analysis is not reliable. When the channel does not provide the source, record "unidentified" instead of guessing.

After the send, the work continues with those who replied and then stopped: see follow-up without pressuring the customer. Anyone already losing contact with leads before Black Friday should fix how leads get lost on WhatsApp first.

Frequently asked questions

Sources

Can I send the offer to all my old customers?

Not automatically. A past purchase is not opt-in for a promotion. Send a new invitation through an approved template or inside an active conversation, ask whether the person wants to be notified, and record the answer. Whoever does not reply stays out of the send on the day.

How far in advance should I start the list?

Three to four weeks before, to invite, clean, and segment. The free 72-hour window expires fast: anyone who joined in October will receive a paid template in November. Plan an action on the day that gets the person to write to you, opening the 24-hour window.

Does the app's broadcast list work?

For small volumes, yes, but the app only delivers to people who saved your number, and you have no source or history per contact. From a few hundred people onward, the Platform with an approved template and a CRM that records opt-in and source give you control over who received, replied, and bought.

What should the invitation message say?

Say what the person will receive, when, and how to leave. Example: "We'll open the Black Friday prices on Friday at 8 a.m. Want to get the list here? Reply YES. To stop, send STOP." The message on the day must deliver exactly what the invitation promised.